This invention relates to a process for chlorinating polyethylene in aqueous suspension while simultaneously grafting a cure site monomer onto the polymer backbone.
When polyethylene is chlorinated, the crystalline thermoplastic starting material is converted to an amorphous chlorinated elastomeric polyolefin. The resultant product can then be cured to give useful products which are resistant to ozone, oxidizing chemicals, light and heat. Such curing is usually carried out by highly reactive reagents, especially peroxides. Due to the inherently nondiscriminating nature of peroxide curatives, various customary additives, for example, certain fillers, such as acid clays and silicas, and plasticizers cannot be incorporated in the compounded polymer. Also, peroxides are hazardous to handle and they have a deleterious effect on commonly used antioxidants and processing oils. It is generally more desirable to incorporate cure sites on the polymer molecule which permit the curing reaction to take place under milder conditions and with a wider choice of curing conditions and compounding ingredients. Such reactive cure sites can be incorporated into chlorinated polyethylene by the chlorosulfonation reaction disclosed in, for example, U.S. Pat. No. 3,299,014 or by grafting maleic acid derivatives onto polyethylene during chlorination as described in, for example, British Pat. No. 773,922. However, these processes must be carried out in organic solvents, such as carbon tetrachloride, which presents disposal and environmental pollution problems. Substitution of an aqueous medium for an organic solvent medium has not been possible due to the solubility of the reagents in water or reactivity of the reagents with water.
The present invention provides a process for making a chlorinated polyethylene elastomer having cure sites on the polymer that are derived from alkyl or alkylaryl monoesters of butenedioic acid by simultaneous chlorination and grafting reactions in an aqueous suspension. The resulting chlorinated polyethylene elastomer that has cure sites grafted onto the polymer backbone can be cured with polyepoxides, polyamine compounds and polyamine generators to give a product which exhibits the desirable properties associated with peroxide cured chlorinated polyethylene elastomers.